Electronegativity Equalization and the Electronic Structure of Polyhedral Clusters of Main-Group Atoms

The concept of the equalization of atomic electronegativities accompanying molecule formation is applied to a study of the electronic structure of polyhedral clusters of main-group atoms such as Ge, Sn, Pb, TI, and Bi. Emphasis is placed upon charged clusters such as Sn9-,Pb:-(x =0+9), Sn+,Ge;-, Sn8-= Pb,T15-, Sn,Bii-, SnTei-, etc. The role of the relativistic spin-orbit splitting of an np shell into np, , , and np3, , subshells in modifying atomic and hence molecular electronegativities is discussed. Correlations are made between calculated charge distributions and observed'99 Sn NMR chemical shifts for clusters of a given size and charge. It is concluded that a useful picture of charge distributions in these clusters may be obtained from electronegativity equalization considerations.